.. 19 PW 813 CRX ANA ST " . . "W ! I ORNL UNCLASSIFIED HAL YTJ MR . . im . " . . ," h Piliin: . iicliniriin.3.: :0 :-COM:5:7, Osiuni 0:Protection Against Radia!!!.."; i love the mainili: .. .,'785.0.2, 0.10er 17-1', 1?. ORNU-P-813 MASTER COPY na - LOTIEP SPECTRA OF GAMMA RAYS PRODUCED BY INTERACTION OF ~ 160-Mevlarong PROTONS WITH Be, C, 0, Al, co, AND Bi* DEC 30-1964 W. Zobel, F. C. Maienschein, and R. J. Scroggs Oak Ridge National Laboratory Oak Ridge, Tennessee CONE-7200/2 The nuclear secondaries produced by the interaction of high-energy pro- tons with nuclei are of interest since protons are the most abundant of the charged particles present in space which present a hazard to manned space travel. Spacecraft shields that are preseritly envisaged as necessary for protection on interplanetary flights are of such thickness that nuclear interactions in the shield become important with respect to ionization produced by the primary pro- tons. The secondaries may be uncharged, making them more penetrating than the primaries, and they may produce a greater biological damage. Thus their produc- tion and transport in the spacecraft shield or structure must be carefully assessed. As part of a larger effort to study secondaries, ? measurements were made of the gamma rays produced in several materials, by 160-MeV protons from the Harvard University Synchrocyclotron. The targets were chosen to cover a wide range in 2 and included Be, C, H20, A1, co, and Bi. Their specifications are given in Table I. Previous measurements include an extensive set by the Oxford group2-5 who used the Harwell Synchrocyclotron. A single NaI(Tl) crystal spectrometer , - - - was used to study the gamma-ray spectra obtained with targets ranging from Li to Ca. Unresolved backgrounds were ascribed to neutron effects, and cross sec- tions were determined for specified gamma-ray energies. Typical cross sections are a few millibarns. *Research sponsored by the National Aeronautics and Space Administration (NASA Order R-104) under Union Carbide Corporation's Contract with the U.S. Atomic Energy Commission. al WE Table I. Target Specifications Diameter (cm) Material Thickness (g/cms) Energy Loss in Target (MeV) Be 7.6 6.055 + 0.030 27.4 - 1.2a 27.4 + 1.6 It 7.6 6.002 4: 0.030 5.10 + 0.05 HOO 7.6 30.1 + 1.48 30.0 + 20 29.1 + 1.62 6.808 + 0.034 7.6 3.224 + 0.0.16 11.16 + 0.56 Bi 7.6 4.505 + 0.023 11.36 + 0.210 a. Calculated from dirference in range, using linear interpo- lation of data given by R. M. Sternheimer, Phys. Rev. 115, 137 (1959). Calculated from difference in range, using curves by M. Rich and R. Madey, Range Energy Tables, UCRL-2301 (1954). C. Calculated using dE7pdx data of Sternheimer (see footnote a) for Cu. d. Calculated using de/pdx data of Sternheimer (see footnote a) for Pb. For the measurements described in this report, the gamma-ray spectrometer requirements were considered to include ascertainable absolute efficiency, high neutron rejection, and an adequate response function (peak-to-total ratio). Multiple-crystal spectrometers were chosen in spite of their attendant complexi- ties and the requirement for experimental efficiency calibration. A three- crystal pair spectrometer was used above 2.0 MeV and an anticoincidence spec- trometer below 2.5 MeV in order to meet the last two requirements. In addition, a time-of-flight requirement was established in order to discriminate against neutron-induced effects. The spectrometer is shown in Fig. 1. The output of the spectrometer is, of course, a pulse-height spectrum which must be "unscrambled" to obtain the corresponding photon spectrum. The unscrambling method used on our data is that of Burrus. It yields an upper and lower bound to the 68% confidence interval connected with the "true" value. The data were divided by the fractional solid ang.le subtended by the detector, the number of incident protons, and the target thickness. The effect of chance coincidences in the pair spectrometer runs were subtracted by measuring the total number of chance coincidences and assuming that their distribution was similar to that of the foreground spectrum. Neutron contributions to the total absorption spectrometer runs were measured by closing the collimator with 12-3/4 in. of lead and subtracting the resulting spectrum from the one obtained with the open collimator. Corrections of < 1.19 + 0.09 for variations in the spectrometer efficiency were applied to the data. A constant correction of 0.94 + 0.02 for the efficiency of the fast, coincidence circuit was made. It was discovered later that this correction varies rather strongly with energy due to the "walk" of the fast signal in the "A" channel. Since the exact energy dependence was not measured, the correction is not made in the spectra presented here. An additional uncertainty of +30% must be ascribed to the results from this cause. Also not shown in the spectra is a correction for the absorption of the gamma rays in the target itself; however, this correction was applied to the cross sections calculated from the data. A correction for the count losses existing in the pair mode of the spec- trometer, amounting to < 2.14 + 0.73, is included in the spectra presented. An analogous correction for the data taken in the total absorption mode was not attempted. Counts lost in the side channels would result in a gain of anti- cuincidence counts, but the spectrum of these counts is distorted to lower energies with respect to the true spectrum. Counts lost in the center channel - - - - do not introduce such a spectrum shift. The governing loss, however, is not in the electronics of the center channel but in the multichannel analyzer. It is difficult to obtain a good correction for this loss. Only an approximate cor- rection (1.0 + 0.2) could be obtained. This was not applied to the spectra shown, but is included in the cross-section calculations. Data taken at 136° to the direction of the incident proton beam, with a separation distance of 104.1 + 0.5 cm between the center of the central crystal and the target center, are presented in Figs. 2-7. Since the unscrambling program only gives the bounds of the 68% confidence interval; hence, only this confidence band is shown. Tables II-VI summarize the results for the different targets. They in- clude the measured energy of the photon, the cross section for its production, corresponding data from the Oxford group where such data have been reported, and possible transitions giving rise to the gamma rays observed. In some entries, two values are shown for the same transition. These represent measurements made with the spectrometer both in the total absorption mode and in the pair mode. Since there is essentially no line structure noticeable in the data from a Bi target, no cross sections were determined for this case. Table VII shows a comparison of calculations by Bertini? of the total nonelastic cross section with our measured cross sections for the production of photons with energy in excess of 600 keV. We also made some measurements, using only the Al target and the spec- trometer in the total absorption mode, at 44º with a separation distance of 102.8 + 0.5 cm, and at 20.50 with a separation of 155.9 + 0.5 cm. The results, together with those from the run at 136°, are shown in Fig. 8. It is seen that Table II. Measured Energies and Cross Sectivliü of Gamma Rays from a Beryllium Target Bombarded by ~ 160-MeV Protons Possible Transition Ex (Rev) measured o (mb) Measured Spectrometera Reaction Energy H Be(P, 2p) L1 987 H H 987 +10 1447 + 10 1536 + 10 1718 1 15 1878 + 15 2069 + 15 H Be(p, 3pn)He 1710 H H 1.69 + 0.63 0.18 + 0.10 0.15 + 0.10 0.28 + + 0.14 0.27 + 0.15 0.24 + 0.13 +0.91 0.72 + 0.34 0.40 + 0.20 0.42 + 0.25 0.46 + 0.22 2184 Be(p,a) Li Belp,Q) Li B + 3560 A A Be(p,Q) Li 5350 4390 1 38 5225 + 30 5675 + 25 6250 + 35 A A Be(P,0) Li* *Denotes transition between excited states. a. In this and the following similar tables T = total absorption mode and P = pair mode. Table III. Measured Energies and Cross Sections of Gamma Rays from a Carbon Target Bombarded by ~ 160-MeV Protons Possible Transition Ey (keV) Measured o (mb) Measured Spectrometer Oxford Group Reaction Energy I 717 н 4.5 + 0.5 1.8 + 0.2 C(p, 2pn) - 3 C(p,4.pn) L. н н 3.9 + 0.4 C(p, pn)ac 1990 е 2872 0.9 + 0.4 н н 695 + 17 7.13 + 2.60 980 + 18 3.55 + 1.33 1982 27 8.51 + 3.12 2014 + 40 5.44 + 1.99 † 35 1.72 + 0.63 3335 + 36 2.00 + 1.37 1.64 + 0.61 4480 + 50 10.9 + 4.1 4470 + 15 11.4 ° 4.1 4930 + 35 4.08 + 1.46 67508 3.03 + 1.09 8795 + 50 0.37 + 0.15 3368 1+ и C(p, 2pn)*B* 2870 C(p, 3p)".BE 12 C(p,p') tac 16C(p, 2p) 433 · 4460 12 C(p, 2p) 453 5030 4433 н 6.6 + 1.0 и н 2.3 + 1.0 2.1 + 0.7 и и 18C(p, 2p)-33 8920 *Denotes transition between excited states. a. Average energy for several gamma rays; not resolved. . Table Iv. Measured Energies and Cross Sections of Gamma Rays from & Water Target Bombarded by ~ 160-MeV Protons Possible Transition E, (keV) Measured o (mb) Measured Spectrometer Oxford Group Reaction Energy I E 3.9 + 1.0 1.7 + 0.5 ELE 180(p,&2pn) 1 B 180(p, 2pn) 249* 2801p, 2p) 25x* 717 2.634 2034 E 727 1 10 1668 + 10 2060 + 10 2392 + 10 2320 1 25 3720 + 30 4430 + 30 3.25 + 1.24 4.4 + 1.8 1.7 + 1.3 2.5 + 1.4 6.7 3.0 2.8 + 1.3 15.8 + 5.7 2.9 + 0.8 280(p, 2pn) 2.311 2311 2 + A 3680 4433 4 5240 5260 + 25 12.0 + 4.9 P 190(p, 3pn) -20 8.3 + 1.7 160XP, par) 22.0 160(P, pn) 150 2.6 + 0.7 160(p, 2p) 250 22.7 + 3.0 180(p, 2p) 25N 2.8 + 0.7 180(p,p') 20 A 6290 + 35 7100 + 50 55.6 1 19.7 12.3 + 4.4 5276 6328 7220 A *Denotes transition between excited states. . : .. - - - . . - - . . - - - - ... - - -. - - . . - . .. . .. ma - - : .. niv - -- . O . D .. -------... w -- . Av - .* r .- H Table V. Measured Energies and Cross Sections of Gamma Rays from an Aluminum Target Bombarded by ~ 160-MeV Protons Possible Transition E, (keV) Measured o (mb) Measured Spectrometer Oxford Group Reaction Energy H i + 830 1010 H 845 + 10 1026 + 10 1392 + 10 1677 + 10 1877 12.4 + 5.3 14.0 + 7.7 30.4 + 11.4 21.9 + 8.8 H 1+ 1369 H !+ 1640 13.2 E 1850 1880* + 1 + BA 1 + 11 +2 2341(P, yn) 29 A1* 14 13 2341(p, pn) 28A1* 23A1(0,0)13 MB 18 + 3.5 23A1(P, pn)ISA1* 27-11(p, pn)a9A1 7.1 + 1.7 33A1(p,p'){ZAL 8.8 + 2.2 JA16P, pn) 1941 22A10p,2). Mg* 12A1(p, 2pn Mg 13A1(p, 2pn). Mg* 2A1(p, pn)aAl* 2.A1(p, pn) 29A1* 2250 + 25 2560 + 35 27"0 + 50 3400 + 20 3975 + 25 BA 7.3 + 9.2 7.3 10.7 2.2 + 5.1 6.4 + 6.2 1 + BA 2219 2540 2753 3410 3920 BA . .-' BA . . a . . 4630 + 35 7.0 + 6.2 BA .. 4600 4620 5120 . .. . . 5165 + 50 3.1 + 4.1 BA - - 5140 6140 + 50 5.8 + 4.5 BG 27A1(p, pn) 28A1* 6190 *Denotes transition between excited states. -9. Table VI. Measured Energies and Cross Sections of Gamma Rays from a Cobalt Target Bombarded by ~ 160-MeV Protons Possible Transition E, (keV) Measured o (mb) Measured Spectrometer Reaction Energy 153 + 60 870 1+ El 857 + 12 1264 + 10 1452 + 15 1745 + 20 se colp,n) SNI colp,p') sco 5.CO(p,p') sco a colp,p').Co 1289 1479 E 1+ 28 + 15 1743 Table VII. Measureà Cross Sections for the Production of Garmma Rays Above 600 keV Compared to Calculated Total Nonelastic Cross Sections Cross Section (mb) Material Measured Calculated 196 + 2 233 + 4 6.8 + 1.3 41.4 + 6.3 115 + 22 434 + 97 1.050 + 220 296 + 3 +1 +1 at nt in +1 +1 +Il +27 + 4 732 +5 a. H. W. Bertini, private communication. -. -..v. .10. . there is essentially no difference in the three spectra, indicating isotropic emission of the prominent gamma rays. Preparations are currently in progress for similar experiments In which the incident protons will have (nominal) energies of 70, 35, and 15 MeV.* . . -. .- . .... ... *Since the presentation of this paper, data have been obtained with ~ 34-MeV protons incident on Be, C, H2O, Mg, and Al targets. Analysis of these data is in progress. -21- References DI 1. NPD Space Radiation Shielding Res. Ann. Progr. Rept;. August 31, 1962, ORNL-CF-62-10-29, Rev. 2. A. B. Clegg et al., Proc. Phys. Soc. 78, 681 (1961). 3. K. J. Foley et al., Nuclear Phys. 21, 43 (1962). 4. K. J. Foley et al., Nuclear Phys. 21, 23 (1962). 5. G. I. Salmon et al., Nuclear Phys. 41, 364 (1963). 6. V. D. Bogert and W. R. Burrus, Neutron Phys. Div. Ann. Progr. Rept. Sept. 1, 1962, ORNL-3360, p. 22. 7. H. W. Bertini, private communication. -12- List of Figures Fig. No. Title i Three-Crystal Spectrometer Assembly and Housing. Absolute Gamma-Ray Yield as a function of Gamma-Ray Energy Due to the Bombardinent by 160-MeV Protons of a 29-MeV-Thick Beryllium Target. Absolute Garma-Ray Yield as a Function of Gamma-Ray Energy Due to the Bombardment by 160.-MeV Protons of a 29-MeV-Thick Carbon Target. Absolute Gamma-Ray Yield as a Function of Carma-Ray Energy Due to the Bombardment wy 160-MeV Protons of a 29-MeV-Thick Water Target. Absolute Game-Ray Yield as a function of Gamma-Ray Energy Due to the Bombardment by 160-MCV Protons of a 29-MeV-Thick Aluminum. Target. Absolute Garma-Ray Yield as a Function of Gamma-Ray Energy Due to the Bombardment by 160-MeV Protons of a 12-MeV-Thick Cobalt Target. Absolute Gamma-Ray Yield as a Function of Gamma-Ray Energy Due to the Bombardment by 160-MeV Protons of a 12-MeV-Thick Bismuth Target. UNCLASSIFIED ORNL - DWG 63-1841 ww to general w w A PHOTOMULTIPLIER TUBE B MUMETAL SHIELD C SIDE CRYSTALS ("8" AND "C") D CENTER CRYSTAL ( "A") E SIDE CRYSTAL HOUSING F TUNGSTEN COLLIMATOR G SPECTROMETER HOUSING (LEAD) H MOVABLE SHADOW SHIELD (STEEL) I GAMMA BEAM INCHES UNCLASSIFIED 2-01-058-921 BERYLLIUM TARGET TOTAL ABSORPTION SPECTROMETER AIR SPECTROMETER 10-30.photons .proton-8. kev-1.atomsh.cm2 0 1 2 3 5 6 7 GAMMA-RAY ENERGY (MeV) 8 9 10 11 12 UNCLASSIFIED 2-01-058-922 64 CARBON TARGET 56 TOTAL ABSORPTION SPECTROMETER PAIR SPECTROMETER H 10-30.photons • proton-4.kev-.atoms-1.cm2 MHWWWLW.. ann ITIN UUTUUDI UUUU JOO 8 9 10 11 12 5 6 GAMMA-RAY ENERGY (Mert . ... UNCLASSIFIED 2-01-058-923 TOTAL ABSORPTION SPECTROMETER WATER TARGET PAIR SPECTROMETER 10-30 photons .proton-4. kevl.atoms-4.cm2 minun W - - - - poner duwun 3 . A . 8 9 10 11 .:5 6 7 GAMMA-RAY ENERGY (MeV) UNCLASSIFIED 2-01-058-924 29-MeV-THICK ALUMINUM TARGET (136°) TOTAL ABSORPTION SPECTROMETER W PAIR SPECTROMETER 10-30 photons• proton.kev-l.atoms---cm2 SC 3 6 7 7 GAMMA RAY ENERGY (MeV) 8 9 10 11 12 UNCLASSIFIED 2-01-058-925 COBALT TARGET .atoms.cm2 TO | TOTAL ABSORPTION SPECTROMETER AIR SPECTROMETER 10-29 photons • proton-4. kev 3 4 5 6 7 8 9 10 11 12 GAMMA-RAY ENERGY (MeV) UNCLASSIFIED 2-01-058-926 BISMUTH TARGET 11 TOTAL ABSORPTION SPECTROMETER I 10-29 photons • proton.kev 4. otoms-4.cm2 - . .. _ I - 50 o 0.5 4.0 2.0 2.5 3.0 1.5 GAMMA-RAY ENERGY (MeV) UNCLASSIFIED 2-01-058-937 29-MeV - THICK ALUMINUM TARGET 20° TOTAL ABSORPTION SPECTROMETER Www 10-28 photons • proton-'-kev.otoms-.cm? 2.0 : 10 L 0.5 1.0 1.5 2.0 GAMMA-RAY ENERGY (MeV). 2.5 3.0 DATE FILMED 4/ 1 /65 ! -LEGAL NOTICE This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accu- racy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method. or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, “person acting on behalf of the Commission" includes any em- ployee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor, At 1 E END